The invention relates to a controller for use with a wide range oxygen sensor.
Oxygen sensors are used in a variety of applications that require qualitative and quantitative analysis of gases. For example, oxygen sensors have been used for many years in automotive vehicles to sense the presence of oxygen in exhaust gases, such as when an exhaust gas content switches from rich to lean or lean to rich. In automotive applications, the direct relationship between oxygen concentration in the exhaust gas and the air-to-fuel ratio of the fuel mixture supplied to the engine allows the oxygen sensor to provide oxygen concentration measurements for determination of optimum combustion conditions, maximization of fuel economy, and the management of exhaust emissions.
Wide range oxygen sensors are known in automotive applications which can measure air-to-fuel ratios ranging from 9 to 50, for example. It is known to use a controller for processing signals derived from an oxygen sensor. When a controller is calibrated to operate over the entire wide air-to-fuel range (e.g., 9 to 50), there is insufficient sensitivity in the region around stoiciometry (e.g., air-to-fuel ratio of 14.7). The lack of sensitivity is due to the use of an analog to digital converter for converting the output of the oxygen sensor to a digital value. To obtain a higher sensitivity, a high-resolution analog to digital (A/D) converter is needed. The cost associated with the A/D in a high-resolution context is high. In addition, the A/D converter may take up valuable space as well. Thus, high-resolution A/D converters are not well suited for automotive applications. Therefore, a separate system, or subsystem, that provides more precise air/fuel ratio data is desirable.
A voltage sensing system that has a pair of input leads having a first input lead, and a second input lead each sensing a non-grounded voltage, and an amplifier coupled to the pair of input leads, the amplifier generating an amplifier output voltage in response to a voltage on the first input lead, a voltage on the second input lead and an offset voltage. The system further includes a controller for receiving the amplifier output voltage and determining an operating range, and an offset voltage generator for generating the offset voltage, the offset voltage generator altering the offset voltage in response to the operating range determined by the controller.
An oxygen sensing system using a sample resistance for sensing a bi-directional current coupled to the voltage sensing system.
A method for sensing air-to-fuel ratio including sampling an input voltage drop derived from a pumping current across a sampling resistance. The input voltage is indicative of air-to-fuel ratio. The input voltage drop is amplified in response to an offset voltage to generate an amplified output voltage indicative of air-to-fuel ratio. An operating range is determined in response to the amplified output voltage. The offset voltage is then adjusted in response to the operating range.